The present invention relates to a thermal transfer sheet and printed object, and particularly it relates to a thermal transfer sheet which is able to impart excellent durability to the image of a printed object wherein an image is carried on a base, and to a printed object having an image with excellent durability.
Thermal transfer systems have conventionally been used to form tonal images or monotone images of characters or symbols on bases. The commonly used thermal transfer systems are heat-sensitive sublimation transfer systems and heat-sensitive melt transfer systems.
Of these, heat-sensitive sublimation transfer systems are based on a process which employs a thermal transfer sheet wherein a base sheet carries a dye layer prepared by dissolving or dispersing a sublimation dye used as the coloring material in a binder resin, and after attaching the thermal transfer sheet to a base, energy corresponding to the image data is applied to a heating device such as a thermal head to cause migration of the sublimation dye in the dye layer on the thermal transfer sheet into the base to form an image. Heat-sensitive sublimation transfer systems are excellently suited for formation of tonal images with gradation because they allow control of the amount of migrating dye in dot units based on the amount of energy applied to the thermal transfer sheet.
Many different types of cards, such as identification cards, drivers licenses, membership cards and the like have been used according to the prior art, and such cards contain various information providing clear identification of the owners. In particular, for ID cards it is most important to have facial images together with printed information regarding addresses, names, etc. The data for such cards are recorded with heat-sensitive sublimation transfer systems as described above, since they simplify formation of images, characters and symbols.
However, tonal images and monotone images formed by these heat-sensitive sublimation transfer systems have inferior resistance, including solvent resistance and plasticizer resistance, because of the transferred dye present on the surface, and hence they cannot be used for cards that require degrees of durability, such as ID cards, for example.
A means of solving this problem has been to laminate a polyester film or the like on the formed image. This improves the solvent resistance and plasticizer resistance but can introduce other problems such as impairment of the properties of the printed object bearing the image, for example the folding properties if the printed object is paper, and the magnetic tape or bar code readability if the printed object is a card.
Protective layers have been transferred onto formed images, but conventional protective layers are polymers such as acrylates and polyesters, and their solvent resistance and plasticizer resistance have been inadequate. Also, when resins crosslinked by ultraviolet rays, electron beams or heat are used as protective layers, increasing the crosslinked density can improve the solvent resistance and plasticizer resistance of the protective layer, but there have been problems of poor film cutting properties and occurrence of transfer defects such as tailing during transfer of the protective layer to the image.
In light of the circumstances described above, it is an object of the present invention to provide a transfer sheet which is able to impart excellent durability to images formed on bases, and to a printed object having an image with excellent durability.
In order to achieve this object, the thermal transfer sheet of the invention is characterized by having a protective laminate provided in a releasable manner on at least a portion of one side of a base sheet, the protective laminate comprising a protective layer and an adhesive layer formed in that order from the side of the base sheet, wherein the protective layer contains solvent-insoluble organic fine particles and a binder resin as the main components.
The organic fine particles of the thermal transfer sheet of the invention have a mean particle size in the range of 0.05-1.0 xcexcm.
The thermal transfer sheet of the invention also preferably has a series of dye layers of one or more colors formed in order on the protective laminate side by side on the base sheet. The printed object of the invention is characterized by being provided with a base, an image formed by a heat-sensitive sublimation transfer method on at least one side of the base, and a protective laminate formed so as to cover at least a portion of the image, wherein the protective laminate is formed by transfer using the above mentioned thermal transfer sheet.
According to an embodiment of the printed product of the invention, the base consists of a card base.
According to the invention as described above, a protective layer composed mainly of solvent-insoluble organic fine particles and a resin binder is formed in a releasable manner together with an adhesive layer on a base sheet to construct a protective laminate, the protective laminate having satisfactory film releasing properties, so that upon transfer onto the image the protective layer becomes situated on the uppermost surface, and therefore the image covered by the protective layer has satisfactory resistance to solvents and plasticizers; furthermore, for printed objects wherein an image is formed on a base by a heat-sensitive sublimation transfer system, the protective layer which covers at least a portion of the image imparts excellent durability to the images of the printed objects.